Aneural muscle cell cultures make synaptic basal lamina components.

Abstract

The basal lamina that runs between the presynaptic and post-synaptic membranes at the neuromuscular junction has distinctive functional properties1–3 amd differs in molecular composition from the extrasynaptic basal lamina to which it is attached4,5. In regenerating muscle, synaptic basal lamina can direct the accumulation both of neuronal transmitter vesicles at specific sites near the presynaptic nerve terminal membrane and of acetylcholine receptors (AChRs) in the postsynaptic muscle membrane1–3. Four components that are concentrated in synaptic basal lamina, but are not detectable in extrasynaptic basal lamina, have been recognized. The first is a particular form of acetylcholinesterase (AChE), the A12 or 16S species, which is concentrated at the synapse in rats6,7 and mice8; its distinctive feature is thought to be a long collagen-like tail9 that attaches it to the basal lamina10. Three other components of the synaptic basal lamina have been distinguished immunocytochemically using antisera raised against basement membrane extracts or collagen-rich preparations4. Although it has been previously reported that aneural muscle cell cultures may make the 16S form of AChE11,12, the role of the nerve in the synthesis and organization of the synaptic basal lamina is unknown. We report here that cells of a mouse muscle line, in the absence of nerves, have surface accumulations of each of the four synaptic basal lamina components described above: the 16S AChE, and cross-reactive antigens recognized by each of the synapse-specific antisera.